1. Field of the Invention
The present invention relates to an intelligent transportation system (ITS), and more particularly to a system and method for providing channel information to search channels in an intelligent transportation system (ITS).
2. Background of the Related Art
An intelligent transportation system (ITS) serves radio communication between a roadside unit (RSU) installed by the roadside and an on-board unit (OBU) mounted on a vehicle by using dedicated short range communication (DSRC). The ITS constructs a system operated when a vehicle having the OBU passes a communication zone formed by antennas connected to the RSU, and provides various information and services to the vehicle upon request.
A variety of services are provided by the ITS according to frequency channels allocated to each RSU. Accordingly, when entering the communication zones of the RSU, the OBU searches a channel of the RSU by performing a channel search operation, and performs an initialization process to receive the information or other services.
FIG. 1 is a diagram illustrating the ITS to which the related art and the preferred embodiment of the present invention are both applied.
Referring to FIG. 1, the ITS includes an OBU 10 mounted on a vehicle for transmitting/receiving information through a DSRC, and first to fourth RSUs 21xcx9c24 installed by the roadside for performing radio data communication with the OBU 10. First and second local servers 31 and 32 are connected to the first to fourth RSUs 21xcx9c24 for analyzing traffic information and various data from the first to fourth RSU 21xcx9c24. Additionally, a traffic information providing server 40 is connected to the first and second local servers 31 and 32, and also to another communication network such as the Internet or a public switched telephone network (PSTN), for providing traffic information.
In the ITS, the OBU 10 transmits the collected traffic information to the first to fourth RSU 21xcx9c24. The first to fourth RSU 21xcx9c24 transmit the traffic information from the OBU 10 to the local server 31, and the local server 31 transmits the traffic information from the first to fourth RSU 21xcx9c24 to the traffic information providing server 40 connected to the local server 32 of a different area.
The traffic information providing server 40 analyzes the traffic information from the local servers 31 and 32, and transmits the traffic information to the OBU 10 through the local server and/or the first to fourth RSUs 21xcx9c24, thereby providing appropriate traffic information to a driver.
The traffic information transmitted from the RSU can be analyzed by the local server or the traffic information providing server.
In the ITS, the first to fourth RSUs 21xcx9c24 may respectively have a variety of functions or a special information providing function. In addition, the first to fourth RSUs 21xcx9c24 are provided with information providing channels for each function.
Although the first to fourth RSUs 21xcx9c24 use different channels with a special information providing function, the OBU 10 does not have information on the functions and channels of the first to fourth RSUs 21xcx9c24. Thus, the OBU 10 must monitor and search channels provided by the corresponding RSU 21xcx9c24 in every communication zone of the first to fourth RSUs 21xcx9c24.
FIG. 2 is a flowchart showing sequential steps of a related art method for providing channel information by an RSU.
First, a vehicle having an OBU 10 passes a zone occupied by an RSU (22 of FIG. 1) (S201). Then, the OBU 10 enters a communication zone of a new RSU 23 (S202). Here, the OBU 10 searches a channel of the RSU 23 and performs initialization (S203). The OBU 10 then searches channel information and/or service information on the new RSU 23 (S204), and communicates with the RSU 23 (S205).
In the related art channel search method for the OBU 10, when frame control message channel (FCMC) data, which is included in a frame control message slot (FCMS), is received in a frame structure from the RSU according to the information science technology (IST) specification of the telecommunications technology association (TTA), it is considered that the data is precisely received from a current channel. The FCMS is a slot containing basic information, such as frequency information by the channel.
Thus, when the OBU 10 enters one of the communication zones of the first to fourth RSUs 21xcx9c24, the OBU 10 waits for FCMC data. When the OBU 10 receives the FCMC data from the middle part, it must wait for a next FCMC data. That is, if it does not receive the full frame of data, it cannot use the partially received data. Waiting for the next FCMC data increases time consumption.
Thus, when the OBU 10 receives the FCMC data from the middle part (the frame transmission having begun before the OBU enters the zone), the OBU 10 cannot analyze the data. Accordingly, the OBU 10 must wait to receive the complete FCMC data to search the channel.
As a result, when the kinds of the ITS services and a number of allocated channels are increased, it takes quite a long time for the OBU to search channels of the RSU. Additionally, when the communication zone of the RSU is short and the vehicle is moving quickly, the OBU fails to search channels.
For example, when it is presumed that a time for searching one channel is, on average, 10 ms and there are eight channels, it takes about 80 to 90 ms to search all of the channels. If it is presumed that the communication zone is 10 M long and the vehicle is traveling at 100 Km/h, a time for passing the communication zone is about 360 ms. That is, the time for searching the channels reaches to xc2xc of the time for passing the communication zone.
In the case of services where data are frequently transmitted/received between the RSU and the OBU, such as a tollgate system, the vehicle cannot receive a wanted service after channel search. Moreover, when the vehicle passes the communication zone without completely ending the communication, it may be regarded as an illegal one.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
It is another object of the present invention to provide to a system and method for providing channel information of a roadside unit (RSU) which can reduce a channel search time by transmitting channel information and/or service information of a next RSU from a current RSU to an on-board unit (OBU).
It is another object of the present invention to provide a method for providing channel information by an RSU from an RSU which can reduce communication errors and efficiently use a communication time by enabling a current RSU to transmit channel information of a next RSU to an OBU so that the OBU can be easily informed of channels of the next RSU without searching the channels.
To achieve at least the above objects in whole or in parts, there is provided a method for providing channel information by an RSU, including predicting a proceeding direction of an OBU by an RSU currently communicating with the OBU or a server connected to the RSU, searching or recognizing an RSU managing the predicted OBU and channel information and/or service information of the RSU, transmitting the searched or recognized information of the RSU to the OBU, and communicating between the OBU and the corresponding RSU using the transmitted information, when the OBU enters a corresponding communication zone.
To achieve at least the above objects in whole or in parts, there is further provided a method for providing channel information by an RSU, including searching a communication zone prior to a current communication zone, predicting a direction of movement an on-board unit (OBU) by using information of at least one of a RSU of the prior communication zone and an RSU of the current communication zone, and obtaining information of a next RSU which will manage the OBU.
To achieve at least the above objects in whole or in parts, there is further provided a method for providing channel information of a roadside unit (RSU), including predicting a direction of movement of an on-board unit (OBU) by at least one of a current RSU currently communicating with the OBU and a server connected to the current RSU, searching or recognizing a next RSU that is predicted to next manage the OBU and at least one of channel information and service information of the next RSU, transmitting the searched or recognized information of the next RSU from the current to the OBU, and communicating between the OBU and the next RSU using the transmitted information, when the OBU enters a corresponding communication zone.
To achieve at least the above objects in whole or in parts, there is further provided a system for providing channel information by an RSU including a first RSU covering a first communication zone, and configured to communicate with an on-board unit (OBU), the OBU being in transit from the first communication zone to a second communication zone, and a second RSU covering the second communication zone, and configured to communicate with the OBU when the OBU enters the second communication zone, wherein the first RSU and the second RSU are conterminous, wherein the first RSU provides information of the second RSU to the OBU while the OBU is in the first communication zone, and wherein the OBU uses the information of the second RSU to establish communication with the second RSU upon entering the second communication zone.
In accordance with the preferred embodiments of the present invention, the current RSU predicts the direction of travel of the vehicle having the OBU, and transmits channel information and/or service information of the next RSU to the OBU in advance. The channel search time is thus omitted and time consumption and channel search errors are reduced, thereby improving communication efficiency.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.